I was foolish enough to sign up for one of these plans a few years ago. Fortunately I never have all of my investment eggs in one basket so was paying much less into the plan than the maximum. Once I realised what was happening I cut and ran. I calculate that I have lost circa 10000USD which is enough to be annoying but isn't really life damaging. I now view it as an expensive lesson in expat money management and I will not make the same mistake again.
I work in a field completely unrelated to aviation but I used to be an aircraft engineer and I still maintain my PPL as well as an interest in aviation. I read these pages because often they contain useful advice about general living in Dubai, this thread being an example. Thanks to Yorkshire Pudding and others as it was only after seeing this thread that my suspicions were confirmed that I was being ripped off.
I've not anything else to add other than to reiterate what others have said i.e. do not touch these schemes with a barge pole.